Vinylidene chloride coating composition containing an aromatic polyester and polyester substrates coated with the coating composition

ABSTRACT

A heat-sealable tack-free coating composition comprising a volatile organic solvent solution of 1. A COPOLYMER OF VINYLIDENE CHLORIDE AND AT LEAST ONE OTHER ETHYLENICALLY UNSATURATED MONOMER COPOLYMERIZABLE THEREWITH, SAID COPOLYMER CONTAINING AT LEAST 80% BY WEIGHT OF VINYLIDENE CHLORIDE, AND 2. ABOUT 0.1 TO 6% BY WEIGHT, BASED ON SAID VINYLIDENE CHLORIDE COPOLYMER, OF A LINEAR POLYESTER RESIN PREPARED BY CONDENSING A GLYCOL AND A POLYFUNCTIONAL ACID, AT LEAST 70% BY WEIGHT OF SAID POLYFUNCTIONAL ACID BEING AN AROMATIC POLYFUNCTIONAL ACID. Also polyester substrates, preferably polyester films, coated with the coating composition and a method of improving adhesion bonding between vinylidene chloride coatings and a polyester substrate, preferably a polyester film.

United States Patent 1 Ranck 1 July 22, 1975 [75] Inventor: Ralph OliverRanck, Richmond, Va.

[731 Assignee: E. I. du Pont de Nemours & Company, Wilmington, Del.

I22] Filed: July 6, I973 121] Appl. No.: 377,087

Related U.S. Application Data [63] Continuation-impart of Scr, No.356,442, May 2,

1973, abandoned.

[52] U.S. Cl ..260/28.5 AY; 260/285 A; 260/336 UA; 260/304 R; 260/328 R;

[51 I Int. Cl. C081 29/20; C081 45/32; (08f 45/52 [58] Field of Search..260/336 UA, 30.4 R, 32.8 R, 260/873, 28.5 A, 28.5 AV

3,549,571 12/1970 Berg et a1. 260/873 3,595,824 7/1971 Aylesworth cta1.. 260/873 3,622,439 11/1971 Manne et a1. 161/184 3,630,826 12/1971Rose et a1. 161/190 OTHER PUBLICATIONS Bulletin No. 17, Revised July,1968, Polyester Adhesives," Automotive and lndustrial Products Division,E. l. du Pont de Nemours & Co.

Primary ExaminerAllan Lieberman [57] ABSTRACT A heat-sealable tack-freecoating composition comprising a volatile organic solvent solution of 1.a copolymer of vinylidene chloride and at least one other cthylenicallyunsaturated monomer copolymerizable therewith. said copolymer containingat least 80% by weight of vinylidene chloride, and 2. about 0.1 to 6% byweight, based on said vinylidene chloride copolymer, of a linearpolyester resin prepared by condensing a glycol and a polyfunctionalacid, at least 70% by weight of said polyfunctional acid being anaromatic polyfunctional acid.

Also polyester substrates, preferably polyester films, coated with thecoating composition and a method of improving adhesion bonding betweenvinylidene chloride coatings and' a polyester substrate, preferably apolyester film.

11 Claims, No Drawings VINYLIDENE CHLORIDE COATING COMPOSITIONCONTAINING AN AROMATIC POLYESTER AND POLYESTER SUBSTRATES COATED WITHTHE COATING COMPOSITION CROSS REFERENCE TO RELATED APPLICATIONS Thisapplication is a continuation-in-part of application Ser. No. 356,442filed May 2, 1973, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to polyester articleshaving improved barrier properties and heat sealability, and moreparticularly relates, in a preferred embodiment, to polyester packagingfilms coated with a saran composition.

Polyester films, and especially polyethylene terephthalate filmsoriented by stretching and/or drawing in both directions, are versatilematerials due to their high strengths and general chemical inertness.These films have been somewhat deficient for use in packaging, however,due to their poor heat sealability and relatively high water vaporpermeability.

The term saran applies to a family of vinylidene chloride homopolymersand copolymers with other ethylenically unsaturated monomer(s). Saran isa well known coating material used to impart water vapor impermeabilityand heat sealability to various substrates, including packaging films.When used as a barrier coating on polyester films, however, the saranhas a tendency to delaminate from the film. This delamination hassomewhat restricted the usefulness of saran coated polyester filmsdespite their otherwise excellent properties.

SUMMARY OF THE INVENTION It has now been found that a coatingcomposition containing saran forms a tack-free barrier coating withimproved adhesion to a polyester substrate when the vinylidene chloridepolymer component of the coating contains at least about 80% by weightvinylidene chloride and the coating composition contains about 0.1 to 6%by weight, based on the vinylidene chloride polymer, of a linearpolyester resin prepared by condensing a glycol and a polyfunctionalacid, at least 70% by weight of said polyfunctional acid being anaromatic polyfunctional acid.

Accordingly, this invention provides a heat-sealable tack free coatingcomposition comprising a volatile organic solvent solution of l. acopolymer of vinylidene chloride and at least one other ethylenicallyunsaturated monomer copolymerizable therewith, said copolymer containingat least 80% by weight vinylidene chloride, and

2. about 0.1 to 6% by weight. based on said vinylidene chloridecopolymer, ofa linear polyester resin prepared by condensing a glycoland a polyfunctional acid, at least 70% by weight of said polyfunctionalacid being an aromatic polyfunctional acid.

This invention also provides a polyester substrate, preferably apolyester film, coated with the composition described hereinabove.

This invention also provides, in a process for the manufacture of acoated polyester film wherein a coating composition comprising acopolymer of vinylidene chloride and at least one other ethylenicallyunsaturated monomer, in solvent, is applied to a polyester film,followed by drying of the coated film to remove the solvent, theimprovement wherein bonding between the vinylidene chloride copolymerand polyester film is improved by adding to the coating compositionabout 0.1 to 6% by weight, based on said vinylidene chloride copolymer,of a linear polyester resin prepared by condensing a glycol and apolyfunctional acid, at least by weight of said polyfunctional acidbeing an aromatic polyfunctional acid.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Copolymers of vinylidenechloride and at least one other ethylenically unsaturated monomer arewell known in the art for use in saran coating compositions.Representative monomers useful in preparing these vinylidene chloridecopolymers include: acrylic acid; acrylates such as methyl, ethyl,isobutyl, butyl, and 2- ethyl hexyl acrylates; methacrylates such asmethyl, phenyl, cyclohexyl, methoxyethyl and chloroethyl methacrylate;methyl alpha-chloroacrylate; methyl isopropenyl ketone; acrylonitrile;methacrylonitrile; methyl vinyl ketone; vinyl chloride; vinyl acetate;vinyl propionate; vinyl chloroacetate; vinyl bromide; styrene; vinylnaphthalene; ethyl vinyl ether; N-vinyl phthalimide; N-vinylsuccinimide; N-vinyl carbazole; acrylamide; methacrylamide; phenyl vinylketone; diethyl fumarate; methacrylic acid; itaconic acid; dimethylitaconate; and the like. The most useful monomers fall within thegeneral formula R CH C where R is hydrogen, halogen, or a saturatedaliphatic radical, and X is one of -Cl, Br, F, CN, C H COOH,

l-lC=O, OC H CONH CONI-IR CONR' where R is alkyl.

Copolymers of vinylidene chloride with an ethylenically unsaturatedmonomer are generally described in terms of the weight ratio of themonomer units in the copolymer. For purposes of this invention, thevinylidene chloride content should be at least to obtain a tack-freecoating, and preferably at least 88% for optimum barrier properties. Bybarrier properties is meant that the copolymer is relatively impermeableto water vapor. In general, the vinylidene chloride content should notexceed about 94% as copolymers of higher vinylidene chloride contenthave poorer heat sealability, although they have excellent barrier andtack-free properties. Useful copolymers generally have an intrinsicviscosity of at least 1.3 as measured on a 1% concentration of copolymerin tetrahydrofuran at 25C.

It has now been found that adhesion bonding between a vinylidenechloride copolymer coating, as described hereinabove, and a polyestersubstrate is markedly improved when the coating also contains about 0.1to 6%, and preferably 0.5 to 2%, by weight, based on the vinylidenechloride copolymer, of a linear polyester and resin prepared bycondensing a glycol and a polyfunctional acid, at least 70% by weight ofsaid polyfunctional acid being an aromatic polyfunctional acid. Theimproved adhesion bonding is achieved without unduly affectingrecognized properties of the vinylidene chloride coating such as lowwater vapor permeability and good heat scalability.

Linear polyester resins, which can contain up to 30% by weight of analiphatic polyfunctional acid, are well known in the art and aregenerally prepared by con densing the selected acids(s) with a diol ofthe formula HOCH +CH CH OH where x is to 10. Particularly useful diolsinclude ethylene glycol and propane 1-3 diol.

Generally both the aromatic acid and aliphatic acid, if present, will bediacids to produce a linear polyester. Thus, the aromatic acid isgenerally at least one of naphthalene dicarboxylic acid, isophthalicacid, or terephthalic acid. The aliphatic diacid, if present, isgenerally an acyclic dicarboxylic acid of the formula where X is a chainof 2 to 8 carbon atoms, such as adipic acid, sebacic acid, or succinicacid.

Useful linear polyester resins are capable of forming films and thushave a molecular weight greater than about 500. The molecular weightmust be low enough, however, that the polyester resin is soluble in thesolvent medium selected for the coating composition. Polyester resinswithin this molecular weight range have no plasticizing effect on thevinylidene chloride copolymer as evidenced by similar heat sealtemperature obtained irrespective of the presence of the polyester.

Linear copolyesters disclosed in US. Pat. No. 2,892,747 to John Dye haveproven to be particularly useful in practicing the invention. Thesecopolyesters are trans-esterification products of the lower alkyl estersof terephthalic acid, isophthalic acid, and at least two acyclicdicarboxylic acids such as adipic acid, azelaic acid, and sebacic acid.Commercially available polyesters which can be selected with advantageinclude epoxy modified polyester resins. Other useful polyester resinsinclude Vitel" PE 100 sold by Goodyear Chemical Company.

Conventional vinylidene chloride coating compositions are firstdissolved in a solvent such as tetrahydrofuran, toluene, methyl ethylketone, or mixtures thereof, and then applied to the desired substrate,followed by drying to remove the solvent. Conveniently, the linearpolyester is added to the vinylidene chloride bath, preferably afterhaving been dissolved in the same solvent as is present in the coatingbath. Conventional saran coating additives, such as wax, particulates(talc, aluminum silicates, insoluble polymers, and the like), andantistatic agents can be added prior to or after ad dition of thepolyester resin to the coating bath. Preferably cross-linking agents, ifused, are present in less than 1% based on the total solids weight aslarger amounts can have a detrimental effect on heat seal strength. Thecoating composition is applied to one or more surfaces of the selectedsubstrate using conventional apparatus such as a gravure roll or doctorroll.

The coating composition of this invention is particularly useful forforming a tack-free, heat-scalable barrier coating with excellentadhesion on an aromatic polyester film substrate. Representativepolyester substrates include polycarbonates such as those prepared frombisphenol A; and 2,6 naphthalate polyesters. Preferred substratesinclude polyalkylene terephthalate polyesters prepared by reactingterephthalic acid (or a dialkyl ester thereof) with glycols of theseries HO+-CH ),,OH where n is an integer greater than I but notexceeding 10. Suitable glycols include ethylene glycol, trimethyleneglycol, hexamethylene glycol and the like. Other functional compoundswhich can be reacted with terephthalic acid or with a dialkyl ester ofterephthalic acid to produce linear polyester types, include p-xyleneglycol, hydroquinone, and cyclic glycols. Other polymers which can beused include polyalkylene terephthalate-containing modifiers such asdibasic acids including among others, isophthalic acid, sebacic acid,adipic acid, sulfonated derivatives and the like. In a preferredembodiment, the coating composition is applied to a polyethyleneterephthalate film which has been oriented by stretching in both themachine and transverse direction.

It has also been found that the coating compositions of this inventionadhere to inorganic film coatings, such as aluminum phosphate or ferricphosphate barrier coats. Thus, if desired, one can first provide aninorganic coating on one side of a polyester film and then coat bothsides with the modified saran composition by passing the film through acoating bath, kiss-coating both sides, or by using other conventionalcoating techniques. Polyester surfaces coated with the inorganic coatingand topcoated with the modified saran coating tend, however, to havelower resistance to delamination than polyester surfaces directlytopcoated with the modified saran composition. Therefore heat sealingshould be accomplished on the saran surface directly contacting thepolyesters, particularly when the sealed film will be subjected tostresses.

The films of this invention posses properties which make them admirablysuited for use as packaging materials for foods such as fresh produce,meats, and baked goods, and for household products such as sponges andthe like. In the example that follows, film properties are assessed bytests described in the following paragraphs.

IPV or initial permeability value is a measure of the water vaporpermeability of the coated film using the test set forth in U.S. Pat.No. 2,147,180 issued Feb. 14, 1939. The lPV is a measure of the grams ofwater permeating through square meters of film per hour at 395C. Ingeneral, films having an lPV of I00 or less are considered to havesatisfactory moistureproof qualities.

OPV or oxygen permeability value is measured using an OX-tran 100apparatus commercially available from Modern Controls, Inc. The OPV is ameasure of the cubic centimeters of oxygen passing through lOO squareinches of film surface in 24 hours under an oxygen pressure differenceof 1 atmosphere.

Heat seal strength is measured by cutting a piece of the coated film 4by l0 inches with the grain or ma chine direction of the film running inthe long dimension of the sample into 2 pieces 4 by 5 inches each. The 2pieces are superimposed so that opposite surfaces are in contact andthen sealed together at each end at right angles to the grain byapplying a inch wide sealing bar under carefully controlled conditionsof temperature (100, 1 l0 or C. as indicated), pressure (2p.s.i.) andcontact time (A second). The sealed days at 35 or 81% relative humidity(RH), the latter to test being a more severe test of the quality of thefilm coating.

EXAMPLE 1 Mol Percent Terephthalic acid 40 Isophthalic acid 40 Adipicacid l Azelaic acid I0 Each coating bath is prepared in a liter flaskequipped with a thermometer, stirrer, reflux condenser, and heater.Vinylidene chloride polymer, toluene, tetrahydrofuran, Mistron HGO-55talc, Sunoco 3420 paraffin wax, and aromatic polyester are added to theflask. The flask is heated at 40 to 45C. until the polymer is dissolved.Five coating com- Preparanon of Coatmg Bath positions containing varyingquantities of ingredients The Vinylidene chloride polymer used has thefollowand prepared in this manner are recorded in Table l.

i TABLE 1 COMPOSITION INGREDIENT I 2 3 4 5 Vinylidene chloride polymer(grams) 317.5 31 I 306 301 285 Toluene (cc) 597 597 597 597 597Tetrahydrofuran (cc) I080 I069 I062 I056 I031 Aromatic Polyestcr grams17.8 28.35 40.5 81 WAX (grams) 4.86 4.86 4.86 4.86 4.86 Talc (grams)I.62 1.62 1.62 1.62 1.62

"l'otal weight polyester and tetrahydrofuran solvent; 40% polyester, 60%solvent by weight. Wt polyester as a percentage of wt Vinylidenechloride for compositions I-5 is, respectively, 0, 2.3%. 3.7%, 5.4%. andH.454.

B. Coating of Polyester Film An I I inch solvent coating tower is usedto apply the coating bath to a V2 mil Mylar polyester film moving at 80feet per minute. The coating bath is placed in a dip tank maintained at40C. and transferred to the film by a doctor roll. The doctor rollsetting is 0.003 inch. Inlet and outlet tower temperatures are 130C. and80C. respectively. Inlet and outlet tower air supply is 250 and 300cubic feet per minute respectively.

The coating weight is determined by X-ray analysis and the coatedsamples are tested for heat seal both as is and after conditioning, andtested for water vapor Results are recorded in Tables 2 and 3.

TABLE 2 COATING HEAT SEAL STRENGTH (g/I inch)" IPV, g/IOO M /HR WEIGHT90C./Vz sec/ I00C./% Sec/ I I0C./% sec/ at 395C. COMPOSITION (g/M 2 psi2 psi 2 psi 9I% RH I0O% RH I 3.04 I05 I23 I27 32 31.5 2 3.00 I I67 21 I41 50.5 3 2.82 I73 I70 230 40 47 4 3.08 I45 I82 I87 54.5 58.5 5 2.68 I02203 I43 78 90.5

"Average of 4 test values "'Average of 2 test values TABLE 3 I 20C/sec/2 psi; 35%RH 2 3 4 CONDITIONED HEAT SEALS"'" 120C/ksec/2 psi; 81%RHCOMPOSITION I Ave I Ave I 35 40 35 50 40 45 45 46 2 I30 I I55 IIO I39I55" 255" I" I68 3 230 I75" 300 280" 246 290 I95 290 235 253 4 235 I50"290 I70 2Il I 220 I50" I64 5 I35" I00 200 I 90" I56 I 75 I 80 I40 290I96 "Unless otherwise Indicated. failure is in adhesion of coating tofilm. Superscript a indicates partial failure at coating-to-coating sealand partial failure at coating-to-film adhesion.

The data of Tables 2 and 3 shows that the coating becomes more perviousto water vapor as the quantity of aromatic polyester in the coatingincreases, and that the adhesive strength of coating to film increaseswith increased aromatic polyester content until a peak strength isreached, between compositions 2 and 4, at which point the adhesivestrength decreases with additional aromatic polyester content.

EXAMPLE 2 A colloidal dispersion was prepared by combining 698 grams ofaluminum chlorhydroxide, 412 grams of 86% phosphoric acid and 15.4pounds of water. The dispersion was coated onto one side of a 0.5 milbiaxially oriented, heat set polyethylene terephthalate polyester filmwhich has been flame treated on the side to be coated. The coated filmwas dried in a tower with a counter current air flow of cfm/ft of film.The film was first dried at about 35C. for 8 seconds and then was heatedat about 85C. for 4 seconds. The coated film, after heating, had acoating weight of about 0.15 gram per square meter, an lPV of and an OPVof 0.1 to 0.2.

This film was then topcoated on both sides with a bath containing:

Saran (as identified in Example 1) 300 grams Aromatic polyester resin1.5 grams Aluminum silicate 3.0 grams Paraffin wax (as identified inExample 1) 4.5 grams Toluene 550 cc Tetrahydrofuran 1190 cc ""Vitel PE100 by Goodyear Chemical Co. 'Flat Hydrite D. Georgia Kaolin Co.. kaolinhaving a 4.5 micron median particle size. by weight 100F.. 3 days, 80%RHRoom Temp. 3 days, 35%RH Sample l 260 330 Sample 2 310 I claim:

1. A volatile organic solvent solution of a heatsealable tack-freecoating composition comprising 1. a copolymer of vinylidene chloride andat least one other ethylenically unsaturated monomer copolymerizabletherewith, said copolymer containing at least 80% by weight ofvinylidene chloride,

2. about 0.1 to 6% by weight, based on said vinylidene chloridecopolymer, of a linear film-forming polyester resin having a molecularweight of at least about 500 prepared by condensing a glycol and apolyfunctional acid. at least 70% by weight of said polyfunctional acidbeing an aromatic polyfunctional acid, and

3. wax and particulates.

2. The composition of claim 1 wherein the linear polyester resin is thecondensation product of 1. at least one diol of the formula HOCH +CH CHOH where x is O to 10, and

2. at least one diacid, wherein at least by weight of said diacid is anaromatic diacid and up to 30% by weight of said diacid is an acyclicdicarboxylic acid of the formula where x is a chain of 2 to 8 carbonatoms.

3. The composition of claim 2 wherein the aromatic diacid is at leastone of isophthalic acid and terephthalic acid.

4. The composition of claim 3 wherein the acyclic dicarboxylic acid, ifpresent, is at least one of adipic acid, sebacic acid, succinic acid, orazelaic acid.

5. The composition of claim 1 wherein the coating composition comprisesa volatile organic solvent solution of l. a copolymer of vinylidenechloride and at least one monomer of the formula where R is hydrogen,halogen, or a saturated aliphatic radical, and X is chlorine, bromine,fluorine, CN, C l-l COOl-l, HC O OC l-l CONH CONHR, CONR where R isalkyl, said copolymer containing about 88 to 94% by weight of vinylidenechloride, and 2. about 0.1 to 6% by weight, based on said vinylidenechloride copolymer, ofa linear polyester resin prepared by condensing a.at least one diol of the formula where x is 0 to 10, and

b. at least one diacid, wherein at least 70% by weight of said diacid isat least one of isophthalic acid or terephthalic acid, and up to 30% byweight of said acid is an acyclic dicarboxylic acid of the formula whereX is a chain of 2 to 8 carbon atoms.

6. The composition of claim 5 wherein the coating composition containsabout 0.5 to 2% by weight, based on said vinylidene chloride copolymer,of linear polyester resin.

7. The composition of claim 5 wherein the diol is ethylene glycol.

8. The composition of claim 5 wherein the acyclic dicarboxylic acid, ifpresent, is at least one of adipic acid, sebacic acid, succinic acid, orazelaic acid.

9. The composition of claim 5 wherein the linear polyester is epoxymodified.

10. The composition of claim 1 wherein the solvent is tetrahydrofuran,toluene, methyl ethyl ketone, or mixtures thereof.

11. The composition of claim 5 wherein the solvent is tetrahydrofuran,toluene, methyl ethyl ketone, or

mixtures thereof.

* 1 I! I i

1. A VOLATILE ORGANIC SOLVENT SOLUTION OF A HEAT-SEALABLE TACK-FREECOATING COMPOSITION COMPRISING
 1. A COPOLYMER OF VINYLIDENE CHLORIDE ANDAT LEAST ONE OTHER ETHYLENICALLY UNSATURATED MONOMER COPOLYMERIZABLETHEREWITH, SAID COPOLYMER CONTAINING AT LEAST 80% BY WHEIGHT OFVINYLIDENE CHLORIDE,
 2. ABOUT 0.1 TO 6% BY WEIGHT, BASED ON SAIDVINYLIDENE CHLORIDE COPOLYMER, OF A LINEAR FILM-FORMING POLYESTER RESINHAVING A MOLECULAR WEIGHT OF AT LEAST ABOUT 500 PREPARED BY CONDENSING AGLYCOL AND A POLYFUNCTIONAL ACID, AT LEAST 70% BY WEIGHT OF SAIDPOLYFUNCTIONAL ACID BEING AN AROMATIC POLYFUNCTIONAL ACID, AND
 2. Thecomposition of claim 1 whereIn the linear polyester resin is thecondensation product of
 2. at least one diacid, wherein at least 70% byweight of said diacid is an aromatic diacid and up to 30% by weight ofsaid diacid is an acyclic dicarboxylic acid of the formulaHOOC-CH2-X-CH2-COOH where x is a chain of 2 to 8 carbon atoms.
 2. about0.1 to 6% by weight, based on said vinylidene chloride copolymer, of alinear polyester resin prepared by condensing a. at least one diol ofthe formula HOCH2-CH2-xCH2OH where x is 0 to 10, and b. at least onediacid, wherein at least 70% by weight of said diacid is at least one ofisophthalic acid or terephthalic acid, and up to 30% by weight of saidacid is an acyclic dicarboxylic acid of the formula HOOC-CH2-X-CH2-COOHwhere X is a chain of 2 to 8 carbon atoms.
 2. about 0.1 to 6% by weight,based on said vinylidene chloride copolymer, of a linear film-formingpolyester resin having a molecular weight of at least about 500 preparedby condensing a glycol and a polyfunctional acid, at least 70% by weightof said polyfunctional acid being an aromatic polyfunctional acid, and3. wax and particulates.
 3. The composition of claim 2 wherein thearomatic diacid is at least one of isophthalic acid and terephthalicacid.
 3. WAX AND PARTICULATES.
 4. The composition of claim 3 wherein theacyclic dicarboxylic acid, if present, is at least one of adipic acid,sebacic acid, succinic acid, or azelaic acid.
 5. The composition ofclaim 1 wherein the coating composition comprises a volatile organicsolvent solution of
 6. The composition of claim 5 wherein the coatingcomposition contains about 0.5 to 2% by weight, based on said vinylidenechloride copolymer, of linear polyester resin.
 7. The composition ofclaim 5 wherein the diol is ethylene glycol.
 8. The composition of claim5 wherein the acyclic dicarboxylic acid, if present, is at least one ofadipic acid, sebacic acid, succinic acid, or azelaic acid.
 9. Thecomposition of claim 5 wherein the linear polyester is epoxy modified.10. The composition of claim 1 wherein the solvent is tetrahydrofuran,toluene, methyl ethyl ketone, or mixtures thereof.
 11. The compositionof claim 5 wherein the solvent is tetrahydrofuran, toluene, methyl ethylketone, or mixtures thereof.